Ocean Thermal Energy Conversion is a process using the heat energy that is stored in the ocean. The oceans collect a huge amount of the world’s heat energy. OTEC uses the heat differences between deep and shallow ocean waters to evaporate a fluid to run a steam turbine and generate electricity. These systems require a 20 degree Celsius temperature difference to effectively operate, making them most suited for tropical regions or areas around the equator where solar radiation creates the minimal temperature differential within 1000m depth (“NREL”).

There are a variety of OTEC systems: closed or open, floating, land-based, or shelf-mounted (“NOAA”). Closed systems utilize a fluid with a low boiling point, typically ammonia, and turns this fluid into vapor through heating with warm seawater. The pressure produced by the expanding vapor turns a turbine and results in the generation of electricity. Cold sea water turns the ammonia, identified as the “working fluid” of the system, back into liquid. Open-cycle OTEC systems differ mainly in that they utilize water as the working fluid. Because of this, when converted back into liquid, the seawater desalinized and can be used for a number of beneficial applications such as drinking and agriculture (“Ocean thermal”). In addition to closed- and open-cycle systems , hybrid systems have been developed that integrate the desalinization benefits of the open-cycle system with the increased power output and efficiency of the closed-cycle system to combine the environmental benefits of both.

Due to the constant nature of OTEC’s energy source it operates as a base load rather than an intermittent source like many renewables. It has low thermal efficiency, but the quantity of energy available as temperature differences in sea water is large enough to generate up to 100MW per system (“Technical readiness”). The largest coal plant can generate 4116MW but with harmful emissions.

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The United States Virgin Islands has long been a candidate for installing on shore OTEC renewable energy power plants. On March 5th, 2014, the Ocean Thermal Energy Corporation and the 30th legislature of the U.S. Virgin Islands signed a Memorandum of Understanding in order to move forward with a study to evaluate the potential benefits of installing an OTEC facility.
According to the U.S. Department of Energy’s National Renewable Energy Laboratory there are upwards of 100 countries and territories in the world, including the Virgin Islands, that have conditions appearing favorable for OTEC, as well as SWAC (Sea-Water Air Conditioning). In 2009, after over 30 years and $300 million spent on researching OTEC, the U.S. Government finally issued a report that the program is now technically feasible and is ready for immediate implementation.
OTEC harnesses its power from the sun; eighty percent of the sun’s solar energy is stored in the surface waters of the oceans and by utilizing the temperature differential between the warm surface water and cold deep ocean water we can obtain a source of constant renewable energy. OWEC and SWAC can produce ample amounts of fresh drinking water, greatly decrease carbon emissions, and save significant sums in energy costs. OTE, the Ocean Thermal Energy Corporation, has the largest deep ocean hydrothermal project in the world, which provides clean-energy saving air conditioning for a $3.5 billion luxury resort that opens in December 2014. OTE’s mission is to meet the global demand for its technologies, bringing environmental, social, and economic benefits to millions of people world-wide. It’s processes can yield a large amount of supplemental revenues by providing nutrient-rich deep ocean water through desalination, as well as opportunities for sustainable fish farming and agricultural enhancement projects.

Citation:

Renewable Energy From The Ocean – A Guide To OTEC, William H. Avery, Chih Wu, Oxford University Press, 1994.